Electric cables are generally constituted by a central conductor surrounded by one or several layers of insulation on which various protections or other conductors are applied, the whole being covered by an outer protective sheath.
These types of cables are repaired or connected together in four operations:
Connecting the central conductor(s); PA1 Moulding the insulations; PA1 Reconstituting the protective means; and PA1 Reconstituting the sheath.
The invention relates to a method of performing operations two and four, namely moulding the insulation and reconstituting the sheath.
The following methods of reconstituting the insulation or the sheath are known in the prior art. In a first method, material is added in the form of wrapped tapes or of half shells, then a heated mould is placed thereover and after gelling or vulcanization, the mould is cooled. Another method consists in placing a mould at the required place and the material is injected in a single or multiple operation. If necessary the material is heated, and in all cases, it is cooled. Such repairs generally give satisfactory results; however, the length of these repairs is limited by the length of the available moulds. If the mixture has to be reconstituted over a length greater than that of the longest available mould, several successive moulding operations must be carried out. This leads to lengthy repair cycles with numerous handling operations, while long moulds must be available if too great a number of cycles is to be avoided.
The tolerances of the various parameters of the cycle are extremely narrow, since, for example, the welding of the injected plastics material with that of the cable must not cause excessive swelling or shrinking of the latter.
Several moulding requirements are in oppostion to each other when the moulding are varied and this leads to the acceptance of compromises of a rather fragile nature.
In simple or multiple injections, the motion of the material causes some imperfections in moulding which are difficult or even impossible to overcome, (e.g. decentering the conductor).
British Pat. No. 921 902 proposes repairing the insulation or the outer protective sheath of an electric cable by using a moving mould which includes a cavity that is supplied with molten thermoplastic material, and whose displacement is obtained either by a mechanical drive or simply by the thrust exerted by the molten thermoplastic material on the intact part of the cable insulation or sheath. This method cannot be used to repair a faulty insulation or sheath when the part to be repaired and the adjacent undamaged parts are of substantially uniform diameter.
The aim of the present invention is to provide a method and a device for covering, thickening or repairing an insulated cable which has been damaged or joined, which method and device are capable of being used on a length of cable of substantially uniform diameter and including a damaged or jointed portion.